That super modest and rigid girl is actually a fan of "that stuff"!? Shimomura was living a fun life filled with "dirty talk" with his friends at an all-boys school. "All-boys school is the best!"... he thought, but then suddenly, the school becomes co-ed starting from the new semester!? The school atmosphere changes completely into a solemn one where you can't even say a word about suggestive topics... What's more, the girl sitting next to him, Kiyoura-san, has absolutely no tolerance for such things, and Shimomura's fun school life turns gray in an instant... or so he thought, but she actually has a certain "secret"...?